Grid shield for gas-filled discharge tubes



Feb. 2, 1965 w. L. VROOM 3,168,669

GRID SHIELD FOR GAS-FILLED DISCHARGE TUBES Filed Feb. 7, 1962 FIG. I

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INVENTOR.

w.| VROOM HIS ATTORNEY United States Patent 3,16%,66d GRID HIELD FER GAS-FILLED DISCHARGE TUBES William L. Vroom Newark, N.J., assignor to General ignal Corporation, a corporation of New York Filed Feb. 7, 1962, Ser. No. 171%,699 6 Claims. (Cl. 313-191) The present invention relates to discharge tubes of the grid control type, and more particularly to an improved grid shield therefor.

In grid control gas tubes, a grid shield closely spaced between the grid and the anode and maintained at cathode potential, not only increases the anode to cathode capacitance and heat shields the grid from the hot anode, but also shields the insulators from the collection of vaporized nickel and other vaporizable components and impurities, and reduces the cathode to anode spacing for maximum voltage capabilities.

Heretofore, grid shields were comprised of a single generally circular nickel stamping having a vertical peripheralflange, which shields were supported spaced from the grid by insulating assemblies attached to the shield inwardly of the peripheral flange. These cup-shaped nickel stampings, which were approximately thirty thousandth of an inch thick, tended to warp in such a manner that two diametrical opposite points bent downwardly while the two opposite points which were spaced 90 degrees from the first two points tended to bend upwardly when the entire tube assembly was heated by inductionduring processing. The peripheral flange of these cupshaped grid shields provided little additional stiffening, and these grid shields were disfigured to the point where they were nearly oval in configuration. This warping of the grid shields caused the spacing between the anode and the grid to vary which adversely effected the operation of the tube.

According to the present invention, the grid shield is comprised of a sheet metal structure, which is preferably nickel, and which has two spaced planar or fiat surfaces that are substantially parallel to each other and are attached to one another at their peripheral edge. These grid shields are mounted spaced from the grid by insulating rods which are connected to one flat surface at angularly spaced points inwardly of the peripheral edge. It has been found that grid shields according to the present invention requires several pounds of force to cause any visible deformation, while the grid shields heretofore used could be deformed with only an ounce or two applied to the rim. Moreover, a grid shield constructed according to the present invention has been heated to over eleven hundred degrees centigrade, which temperature is well above the processing temperature, without any visible warping.

One of the objects of the present invention is to provide an improved grid shield assembly which does not tend to warp when heated, thus maintaining an accurate closely spaced relationship between the anode and the grid.

Another object of this invention is to provide an improved grid shield which permits the spacing of the flat or planar portion of the shield to be near the anode to increase the anode to cathode capacitance.

A still further object of the invention is to provide an improved grid shield which does not deform when heated 3,1585% Patented Feb. 2, 1965 and which may be mounted by members fastened to the flat portion inwardly of its peripheral edge.

Other objects of this invention will become apparent from the specification, the drawing and the appended claims.

In the drawing:

FIG. 1 is a sectional view of the tube showing a grid shield according to one embodiment of this invention;

FIG. 2 is a cross-sectional view of the tube taken at line 2-2 of FIG. 1 and looking in the direction of the.

arrows;

FIG. 3 is a cross-sectional view of the grid shield of FIGS. 1 and 2;

FIG. 4 is a cross-sectional view of a grid shield constructed according to another embodiment of the present invention;

FIG. 5 is a cross-section of a grid shield constructed according to still another embodiment of the invention; and

FIG. 6 is a cross-section of a grid shield constructed according to still another embodiment of this invention.

Referring to the embodiments of the invention by numerals of reference, a tube generally referred to at 10 is provided with a conventional cathode assembly 12 having reinforcing strips 14 adjacent its top and bottom. The

cathode assembly 12 is rigidly supported in a glass envelope 16 of the usual type by two still bifurcated uprights 18 which are welded at their upper ends to the reinforcing strips 14 at the bottom edge of the cathode assembly 12. The lower ends of the uprights 18 are welded to a collar 20 which is mounted on a glass reentrant stem 22 of the tube assembly 16. The collar 20 is crimped tightly on the glass stem 22 in :a conventional manner. The cathode assembly 12 is alsoprovided with connecting rods 24, which are welded at their upper ends to the bottom of the cathode assembly 12-, and are bent and anchored in the reentr-ant stem 22 in a conventional" manner. The connecting rods 24 may be connected to suitable leads for external connection.

A grid assembly 25 which is comprised of a circular sheet metal member has a central discharge opening over which a plurality of spaced grid bars 26 are conventionally fastened. The grid assembly 25 is rigidly supported and spaced axially from the upper end of the cathode assembly 12 by insulating assemblies 28, which are comprised of ceramic members having axially spaced grooves for insulating the grid 25 from the cathode assembly 12. A grid connector 30 is attached, as by welding, to the grid assembly 25, and extends downwardly in the assembly 12 for connection at its lower end in a conventional manner, to a rod 32 that extends into the glass stem 22. The rod 32 is connected to a suitable wire for connection to an external source.

An anode 44, which is a thin circular sheet of nickel, and which is formed with an up-turned peripheral flange 45 is spaced above the grid. The anode 4 is rigidly supported in this spaced relationship by a pair of anode leads 46 which are securely fastened in' a glass anode stem 43 of the tube assembly 16. The'upper ends of the leads 4d are connected in the usual manner to wires 49 for external connection. The lower ends of the leads 46 are attached as by welding to the upper portion or" a head radiating fin assembly 50. The fin assembly 5b is fastened to the upper surface of the anode 44 by welding. This anode and its assembly is more specifically described 3 in my copending US. patent application Ser. No. 161,837, filed December 26, 1961, and entitled Improved Anode Assembly for a Discharge Tube, to which reference may be made for a more detailed description thereof.

The preferred embodiment of the grid shield, which is illustrated in FIGS. 1 through 3, is generally referred to at 55. The grid shield 55 is comprised of a circular plane sheet metal member 56, and a sheet metal member 62. The member 56 is preferably nickel, and has an integral upturned peripheral flange 57 to constitute a generally circular cup shaped configuration. The member 56 also has a central opening 58 which is in registry and alignment with the central opening of the grid 25 for communication therewith. The member 56 is provided with four angularly spaced openings in its fiat portion intermediate its peripheral edge which is bounded by the flange 57, and the opening 58. Through each opening extends a supporting rod on which insulating members 60 are mounted to support the member 56 accurately spaced from the grid 25. Eyelet members 61 secure the member 56 securely to the insulating members 6t).

The sheet metal member 62, which is preferably made of nickel, has an up-turned peripheral flange 63 and is so dimensioned that it nests in the cup shaped member 56 so that the outer peripheral face of the flange 63 is in intimate contact with the inner face of the flange 57. The member 62 is further positioned so that its upper edge 64 of its flange 63 is coextensive and lies substantially in the same plane as upper edge 65 of the flange 57. The member 62 is rigidly fastened by its flange 63 to the flange 57 of the member 56 by closely spaced spot welds, preferably eight or more, which are equi-angularly spaced. The member 62 has a central opening similar to the central opening of the member 56 and the central opening in the grid 25, and is in axial alignment therewith. Thus, in accordance with this preferred embodiment, the one cup shaped member 62 is nested in the cup shaped member 56 so that its flat or planar surfaces are in parallel relationship with the members 56 and 62 being attached by spot welding the peripheral flange 63 to the flange 57. The entire grid shield assembly 55 is then supported inwardly of the peripheral edge of the member 56 by the insulating assemblies 60.

Referring to the modification shown in FIG. 4, the grid shield is generally referred to at 70, and is comprised of a lower circular sheet metal position 71 which has an integral up-turned peripheral flange portion 72 with an integral inwardly extending flat portion 73. The portion.

73 is substantially parallel to the portion 71. The shield 70 also has a central opening in its portions 71 and 73 similar to the openings in the grid shield 55.

Another modified form of a grid shield generally referred to at 75 is illustrated in FIG. 5. The grid shield 75 is comprised of a cylindrical flange 76 and a plane sheet metal portion 77, and a plane sheet metal portion 78. The sheet metal portions 77 and 78 are fastened as by welding adjacent the upper and lower edges of the cylindrical flange 76. The members 77 and 78 are provided with a flange portion 80 to provide better contact when welding the members 77 and 73 to the cylindrical flange 76. The members 77 and 78 also have the central opening similar to the other embodiment.

A further modification of a grid shield is illustrated in FIG. 6 and referred to at 82. This grid shield 32 is comprised of a cylindrical flange 83 having upper and lower edges 84 which are bent inward slightly. A plane sheet metal member 85 having a central opening is attached as by welding to the upper edge 84 of the member 83; and a second sheet metal member 86 is fastened as by welding to the lower edge 84 of the flange 83.

In one practical application of the preferred embodiment of the invention illustrated in FIGS. 1 through 3, the outside diameter of the member 56 was approximately 2.189 inches and the central opening was approximately 1.421 inches. The inner member 62 has an outside diameter of 2.180 inches and an opening identical to the opening of the member 56. The width of the flange of the member 56 was .315 inch while the width of the flange 63 of the member 62 was .100 inch. The thickness of each of the members 56 and 62 was .004 of an inch. It has also been found in practice that grid shields herein provide for increased capacitance between the anode and cathode due to the close spacing of the flat portion of the member 62. Such close spacing of previous grid shields was impractical because of the warping tendency during heating. Also, double heat shielding of the grid from radiant energy of the anode is provided.

Thus, it is apparent that I have provided an improved grid shield assembly which may be rigidly mounted in the tube inwardly of its peripheral edge, and yet will not warp when heated, which provides for close and accurate spacing.

Although several specific embodiments of the present invention have been shown and described herein, it is understood that other modifications, adaptations and alterations may be made without departing from the spirit or scope of the present invention.

What I claim is:

1. In a grid controlled gas-filled discharge tube having an anode and a cathode assembly positioned one above the other in spaced relation along the longitudinal axis of the tube envelope, said anode having a plane surface extending substantially normal to said longitudinal axis, and a grid supported by the cathode assembly spacedly mounted between said cathode and the plane surface of the anode, the combination of a grid shield comprising a generally circular sheet metal member having substantially parallel spaced planar surfaces extending substantially parallel to the plane surface of the anode and being interconnected at their peripheral edges by a generally circular flange portion, each of said parallel surfaces having a central opening positioned to provide communication between the cathode assembly and the plane surface of the anode, and means connecting one of the planar surfaces at a plurality of 'angularly spaced points intermediate the flange portion and the peripheral edge of its central opening to the cathode assembly to fix rigidly said grid shield in spaced relation above the grid and below the plane surface of the anode,

2. In a tube according to claim 1 wherein the means connecting the grid shield to the cathode assembly are a plurality of angularly spaced rods extending through the grid substantially normal to the spaced planar surfaces.

3. In a discharge tube according to claim 1 wherein the spaced planar surfaces of the grid shield are integral with the circular flange portion to constitute a grid shield that is substantially U-shaped in cross section.

4. In a grid controlled gas-filled discharge tube having an anode and a cathode assembly mounted one above the other in spaced relation along the longitudinal axis of the tube envelope, said anode having a plane surface extending substantially normal to said longitudinal axis, and a grid supported :by the cathode assembly spacedly mounted between said cathode and the plane surface of the anode, the c-ombination of a grid shield comprising a first plane circular sheet metal member having a peripheral flange portion, a second circular plane sheet metal member having a peripheral flange portion, said first and second members being positioned relative to each other to have their plane portions spaced one above the other substantially parallel to each other and normal to said longitudinal axis, said flange portions being in intimate engagement with one another, means rigidly attaching said members to each other by their flange portions, each of said members having a central opening to provide communication between the cathode and the plane surface of the anode, and means connecting one of the planar surfaces at a plurality of angularly spaced points intermediate the flange portion and the peripheral edge of its central opening to the cathode assembly to mount said grid shield in spaced relation between the grid and the respective flange portions being in intimate engagement plane surface of the anode. with one another.

5. In a tube according to claim 4 wherein the connecting means is a plurality of angularly spaced rods fastened Refwwces Cmd by the Examiner at one end to said planar surface and extending through 5 UNITED STATES PATENTS the grid and attached at their opposite ends to the cath- 1,656,505 7/13 Kraus fit aL ode assembly, said rods extending substantially paralle 2 395 07 3 45 Waims 313 193 to each other and the longitudinal axis. 2,424,293 7/47 Wan-u 313- .193

6. In a tube accordingto claim 4 wherein the one said 7 L f sheet metal member is nested in the other said sheet met- 10 DAVID GA Prlmary t' a1 member with the outer and inner surfaces of their KAI-(LAM, Examiner- 

1. IN A GRID CONTROLLED GAS-FILLED DISCHARGE TUBE HAVING AN ANODE AND A CATHODE ASSEMBLY POSITINED ONE ABOVE THE OTHER IN SPACED RELATION ALONG THE LONGITUDINAL AXIS OF THE TUBE ENVELOPE, SAID ANODE HAVING A PLANE SURFACE EXTENDING SUBSTANTIALLY NORMAL TO SAID LONGITUDINAL AXIS, AND A GRID SUPPORTED BY THE CATHODE ASSEMBLY SPACEDLY MOUNTED BETWEEN SAID CATHODE AND THE PLANE SURFACE OF THE ANODE, THE COMBINATION OF A GRID SHIELD COMPRISING A GENERALLY CIRCULAR SHEET METAL MEMBER HAVING SUBSTANTIALLY PARALLEL SPACED PLANAR SURFACES EXTENDING SUBSTANTIALLY PARALLEL TO THE PLANE SURFACE OF THE ANODE AND BEING INTERCONNECTED AT THEIR PERIPHERAL EDGES BY A GENERALLY CIRCULAR FLANGE PORTION, EACH OF SAID PARALLEL SURFACES HAVING A CENTRAL OPENING POSITIONED TO PROVIDE COMMUNICATION BETWEEN THE CATHODE ASSEMBLY AND THE PLANE SURFACE OF THE ANODE, AND MEANS CONNECTING ONE OF THE PLANAR SURFACES AT A PLURALITY OF ANGULARLY SPACED POINTS INTERMEDIAATE THE FLANGE PORTION AND THE PERIPHERAL EDGE OF ITS CENTRAL OPENING TO THE CATHODE ASSEMBLY TO FIX RIGIDLY SAID GRID SHIELD IN SPACED RELATION BOVE THE GRID AND BELOW THE PLANE SURFACE OF THE ANODE. 